It is observed that a fair amount of physical and chemical adsorbed water is released from solid breeder materials by introduction of dry N2 gas and that not a little amount of water is also continuously produced by the water formation reaction when the purge gas with hydrogen is applied. It is reported by present authors that the water released to the purge gas from solid breeder materials affects the tritium release behavior. The capacity and desorption rate of chemical adsorbed water, and the capacity and rate of water formation reaction for Li4SiO4, which has been supplied from FzK, are quantified in this study. It is found that the overall reaction rate of water formation on Li4SiO4 is larger than the rate observed for other solid breeder materials. Therefore, most hydrogen added to the blanket purge gas changes to water so far as the water formation capacity of Li4SiO4 remains. It is also found that water formation capacity of Li4SiO4 is almost the same as that of Li2TiO3. Tritium release behavior from Li4SiO4 and Li2TiO3 packed in the blanket are compared in this paper using the Kyushu University model and properties obtained in this study.